The present invention relates to a cable according to the preamble of claim 1.
In the field of monitoring and/or controlling oil/gas wells, a cable may be positioned within or attached to the outside of the tubing. The cable extends from the wellhead to various communication nodes, sensors and actuators down hole. Cables of this kind must be able to withstand high temperatures, large hydrostatic pressures and an aggressive environment. In addition, the cable must withstand large mechanical pressures. Experience has shown that cables comprising an optical element, preferably optical fibers, are susceptible to attack by hydrogen from the surrounding environment, the hydrogen penetrating into the optical element, causing an attenuation increase and resulting in communication failure. Therefore, the optical element must be protected against in-diffusion of hydrogen. In the prior art this has been done according to at least one the following solutions:
choosing fibers comprising glass materials which are insensitive to hydrogen in-diffusion,
Use of a barrier of for example metal or carbon outside the fiber, so-called hermetic fibers,
Use of specific materials, e.g. hydrogen scavenging greases, which capture/tie up free hydrogen,
Using tube enclosures of metal or plastic that act as barriers preventing or delaying in-diffusion of hydrogen.
The present invention aims at protecting the optical element against the in-diffusion of hydrogen, possibly in combination with one or more of the above mentioned techniques.